Geography - Rivers

• River deposition is the process by which sediment carried by a river is dropped or deposited when the river's velocity decreases.
• Roles of Rivers

  Erode, transport, create new landforms
• Upstream Changes

  Increased/more Erosion

  Decreased/less Deposition

  Bigger load particle size

  Higher/increased gradient

  Lower/less/decreased Discharge

  Decreased/less water velocity
• Downstream Changes

  Decreased/less Erosion

  Increase/more Deposition

  Smaller load particle size

  Lower gradient

  More/increased Discharge

  Increased/higher water velocity
• Potential Energy

  Weight and elevation of the water.
• Kinetic Energy

  Gravity and flow of the water.
• Channel Shape

  the bigger the hydraulic radius, the more efficient water movement
• Channel Roughness

  Causes friction

  The higher the ratio, the more efficient the water flow.
• Drainage Basin

  Water is supplied by precipitation.

  Water is drained by river and its tributaries.

  Drainage basins are divided by watersheds.
• Tributaries

  smaller rivers that join the larger river.
• Confluence

  The point where the smaller river joins a larger river.
• Watershed

  the area that drains into a single river
• Hydrological Cycle

  movement of water between atmosphere, lithosphere and biosphere

  (globally) closed system with no water loss

  (locally) single input, 2 major outputs
• Water Storage

  • Vegetation
  • Surface
  • Soil moisture
  • Groundwater
  • Water channels
  • Oceans and atmosphere (global scale)
• Types of Rainfall

  • Cyclonic: uplift of air within a low-pressure area (warm air rises over cold air);low to moderate intensity rain and last a while
  • Orographic: deep layer of moist air forced to rise over range of hills or mountains
  • Convectional: Heating causes pockets of air to rise and cool
• Types of River Erosion ( HAAS )

  • Abrasion : Wearing away of bed and bank by load carried by the river.
  • Attrition: Wearing away of the load carried by river, which creates more but smaller particles
  • Hydraulic action: Force of air and water on the sides of rivers and in cracks
  • Solution : the removal of chemical ions, which causes rocks to dissolve
• Interception

  • Interception loss: water retained by plant surfaces and later evaporated away or absorbed by the plant
  • Throughfall: Water that fails through gaps in vegetation, drop from leaves
  • Stemflow: Water that trickles along branches and down the trunk.
• Evaporation

  Process when liquid or solid changes into gas. 

  Biggest source is the sea and oceans.

  It increases with warm, dry & windy conditions.
• Evapotranspiration

  Transpiration is the process when water vapour is transferred from vegetation to atmosphere. 

  Combined effects of evaporation and transpiration is referred to evapotranspiration.

  Evapotranspiration accounts nearly 100% of removal of annual precipitation in arid areas and 75% in humid areas
• Infiltration

  It is the process by which water soaks into the ground. 

  The infiltration capacity is the maximum rate at which rain can enter the ground.
• River Process

  Erosion

  Transportation

  Deposition
• Factors Affecting Erosion

  Load: The heavier and sharper the load the greater the erosion

  Velocity and discharge: The greater the velocity and discharge the greater the erosion

  Gradient: Greater gradient, greater erosion

  Geology: The more unconsolidated the rock, the faster the erosion

  pH: rate of solution increases with lower pH(higher acidity)

  Human impact: deforestation, building dams and bridges interfere river flow and increase rate of erosion
• Ways of Transportation

  • Saltation: heavier particles bounces and bumps along river bed
  • Solution: chemical load is dissolved in the water
  • Suspension: small particles are held by turbulent flow of river
  • Traction: Heaviest material is dragged or rolled along the river bed
  • Flotation: leaves and twigs are carried on surface of river
• Deposition


  Deposition occurs as river slows down and loses energy. The larger heavier particles are deposited first, followed by the lighter particles.
• What are Potholes caused by? ( erosion )

  Hydraulic action and abrasion
• Where in the river stream do you think you will find Pothholes?

  Upper and Middle
• How is a waterfall formed?

  • Frequently occurs on horizontally bedded rocks (usually hard and soft rocks)
  • Over time, rapids can be formed. 
  • Plunge pool may cause waterfall to migrate upstream.
• What type of erosion happens when making a waterfall?

  Hydraulic Action

  Abrasion

  Attrition
• How are Gorges formed?

  Formed where rocks are resistant to weathering but susceptible to more powerful river erosion.
• Oxbow Lake


  a result of erosion and deposition.
• Floodplains


  Area covered by water when a river floods. Natural regulation of the sediments deposit in river channel. 
• Levees


  When it floods, speed reduced, sediments are deposited, heaviers one near river bank, lighter in floodplains.
• Optic Nerve


  The nerve that carries electric signals from the eye to the brain.
• Sclera


  The white, tough outer layer that protects the eye.
• Macula


  A small, specialized area at the back of the retina responsible for central vision.
• Retina

  The innermost layer of the eye containing rods and cones.
• Lens


  A clear disk behind the iris that changes shape to focus on objects at different distances.
• Iris


  The colored part of the eye that controls the amount of light that enters.
• Cornea


  The transparent outer layer of the eye that allows light to enter.
• Blind Spot


  Where the optic nerve leaves the eye (no cones or rods).